Ha. Armstrong et Al. Coe, DEEP-SEA SEDIMENTS RECORD THE GEOPHYSIOLOGY OF THE LATE ORDOVICIAN GLACIATION, Journal of the Geological Society, 154, 1997, pp. 929-934
Sedimentological analysis of the Ordovician-Silurian international bou
ndary stratotype section at Dob's Linn, Scotland shows systematic chan
ges in muddy turbidite microfacies which are interpreted in terms of a
four phase glaciation. This comprised: (1) a, pre-glacial cooling of
the deep sea in the early Ashgill (Cautleyan), (2) initiation of inten
se thermohaline circulation in the late Rawtheyan, predating, (3) the
start of the glacial maximum near the end of the Rawtheyan, and (4) ra
pid de-glaciation in the mid- to upper Hirnantian (lower part of the p
ersculptus Biozone). It is proposed that the glacial maximum was trigg
ered by a combination of negative greenhouse effect ('Monterey Hypothe
sis') and increasing surface albedo. Cessation of thermohaline circula
tion and the expansion of anoxia mark the rapid end of the glaciation
in this deep-sea environment.